Can I use the same sending domain with multiple ESPs?

Key findings

• Technical feasibility: It is possible to use the same primary domain across multiple ESPs.
• Subdomain necessity: You cannot use the exact same subdomain for the RFC 5321.From address across different ESPs; each requires its own unique subdomain for proper bounce handling and click tracking.
• DNS records: SPF, DKIM, and DMARC records must be correctly configured to authorize all sending sources for the domain. This often involves adding multiple email authentication entries to your DNS.
• Gradual migration: This approach enables a phased migration, allowing for IP warming on the new ESP while maintaining operations on the old one, thus preserving sender reputation.

Key considerations

• DNS complexity: Managing multiple SPF, DKIM, and DMARC records can become complex, increasing the risk of misconfigurations that could impact deliverability.
• Bounce and FBL handling: Ensure that each ESP is properly configured to handle its own bounces and feedback loops (FBLs) via unique return-path domains (RFC 5321.From).
• Click tracking: Different subdomains will be required for click tracking, as each ESP typically uses its own infrastructure for this purpose.
• Sender reputation management: While the domain reputation can be shared, the reputation of individual IPs within each ESP still needs to be managed through careful warming and sending practices. Consider the risks associated with shared sending domains.

Key opinions

• Phased migration: Many marketers prefer to slowly shift email volume from an old ESP to a new one, allowing for gradual IP warming and continued operation of existing campaigns.
• Reputation preservation: The ability to transfer or retain domain reputation is a significant driver for wanting to use the same sending domain.
• DNS configuration concerns: There is a common concern about the complexity of managing DNS records for multiple ESPs on the same domain.
• ESP compatibility: Marketers generally expect ESPs to support this type of setup, as it is not an uncommon request.

Key considerations

• Authentication setup: Ensuring proper SPF, DKIM, and DMARC alignment for each ESP is critical to avoid deliverability issues. This often involves deciding whether to use the same or different subdomains for each.
• Reporting and analytics: Marketers need to consider how to consolidate or view reporting from multiple ESPs to get a holistic view of campaign performance.
• Campaign coordination: Careful planning is needed to avoid sending duplicate emails or overwhelming recipients when transitioning campaigns between ESPs.
• Support engagement: It is advisable to engage with ESP support teams early to discuss multi-ESP domain setup, as they are often familiar with these requests. More details on using multiple ESPs safely can be found in this article on best practices.

Key opinions

• Unique subdomains are paramount: While the root domain can be shared, specific subdomains are required for elements like the Mail From (RFC 5321.From) address and click tracking to ensure proper functionality and attribute bounces correctly.
• DKIM selector variation: Using different DKIM selectors for each ESP is a best practice to allow multiple entities to sign emails on behalf of the same domain without conflict.
• ESPs are prepared: Most reputable ESPs are accustomed to and equipped to handle configurations involving shared sending domains across multiple providers.
• Alignment is key: Proper SPF, DKIM, and DMARC alignment for each sending source is crucial for deliverability and reputation.

Key considerations

• DMARC policy enforcement: When using multiple ESPs, DMARC becomes even more critical for monitoring authentication and ensuring all legitimate sources are aligned. Learn how to set up DMARC with multiple senders.
• Collaboration with ESP support: Engage with the deliverability teams of both ESPs to ensure seamless setup and troubleshooting, as they are typically familiar with such scenarios, as confirmed by AWS support discussions.
• Monitoring and troubleshooting: Implement robust monitoring to detect any authentication or deliverability issues stemming from the multi-ESP setup and be prepared to troubleshoot SPF authentication issues efficiently.
• Subdomain strategy: Plan your subdomain strategy carefully, dedicating specific subdomains for each ESP to manage bounce processing and unique click tracking requirements effectively.

Key findings

• SPF record requirements: Your SPF record must include all IP addresses or domains of every ESP authorized to send email on behalf of your domain. Missing entries will lead to SPF authentication failures.
• DKIM unique selectors: Each ESP will likely provide its own DKIM keys, requiring you to publish distinct DKIM selectors for each on your DNS. This allows for separate authentication paths without collision.
• DMARC for oversight: DMARC policies are essential for instructing receiving servers on how to handle emails that fail SPF or DKIM authentication from your domain, providing aggregate reports on all sending sources.
• Subdomain configuration: Many ESPs recommend or require custom subdomains for bounce addresses and click-tracking, which are typically managed via CNAME records pointing to the ESP's infrastructure.

Key considerations

• SPF 10-lookup limit: Be mindful of the SPF 10-lookup limit; exceeding this can cause authentication failures. Combining or flattening SPF records might be necessary for complex multi-ESP setups. If you're experiencing issues, explore how to resolve SPF TempError.
• DMARC alignment: Ensure both SPF and DKIM authenticate and align with your 'From:' domain to pass DMARC checks, which is essential for maximizing deliverability when using multiple senders on the same domain.
• Consistent 'From:' address: While subdomains may differ, maintaining a consistent RFC 5322.From (header From) address across all ESPs strengthens brand identity and user recognition.
• BIMI compatibility: For brands using BIMI, the documentation indicates support for selectors, enabling the same domain to publish multiple, separate BIMI records for different sending setups, as noted by BIMI Group FAQs.